We propose a collaborative, population-based case-control study of modifiable risk factors for prostate cancer among blacks, whites and Asians in Los Angeles, San Francisco, Hawaii, Vancouver and Toronto. Investigators will use a common protocol and questionnaire to administer personal interviews to approximately 500 black patients, 500 white patients, and 500 Asian patients with histologically confirmed carcinoma of the prostate, and 1500 black, white and Asian population-based controls. Controls will be matched to cases on age, ethnicity and region of residence. The information requested from subjects will permit: a) testing of hypotheses relating age- and ethnic-specific prostate cancer risks to diet, physical activity levels and body mass index; b) examination of ethnic and age differences in distribution of etiologic factors and in relative and attributable risks for etiologic factors; c) estimation of the fraction of interethnic rate differences attributable to differences in distributions of etiologic factors and to differences in relative risks for specific etiologic factors. Serum collected from a subsample of 600 control subjects will be analyzed for levels of sex hormones and prostate-specific antigen (PSA), a marker for prostate cancer and/or benign prostatic hypertrophy. These analyses will permit testing of hypotheses relating diet, physical activity and body size to serum hormones and to subclinical prostatic disease within and across ethnic subgroups in the population. They also will allow comparison of lifestyle characteristics of cancer cases to those of controls 'without abnormal PSA levels, an exciting new tool in prostate cancer research. The project has the following strengths: it offers a unique opportunity to .elucidate the etiology of a major cancer using populations heterogeneous in lifestyle characteristics and prostate cancer rates; it addresses the roles of modifiable characteristics in accounting for heterogeneity of prostate cancer rates in these diverse populations; it will assess subclinical prostatic disease in these populations and relate it to lifestyle characteristics and hormone levels; it involves investigators experienced in epidemiologic assessment of diet and physical activity who have collaborative experience among themselves and with others; it builds upon prior prostate cancer research by members of the group.